1. Field of the Intention
The present invention relates to a motor-vehicle starter.
The invention relates more particularly to a starter of the type including an electric motor the output shaft of which rotationally drives a coaxial inertia-type drive with the interposition of a step-down planetary-meshing gear train.
2. Discussion of the Related Art
In order to limit the value of the maximum torque which can be transmitted between the output shaft of the electric motor and the shaft of the inertia-type drive, it is known to provide a torque-limiter device.
To that end, a friction-type torque-limiter device has already been proposed, in which at least one friction disc is pressed by an elastic element against an annular, side face of the crown ring of the step-down planetary gear train of the starter, the other face of the crown ring being in contact with a second friction disc. Moreover, the friction disc is linked in rotation to the casing.
The pressure exerted by the elastic element on the friction disc makes it possible to limit the torque to which the crown ring of the planetary gear train is subjected. This is because, when the torque is greater than the resisting torque which is due to the friction between the friction disc and the crown ring of the planetary gear train, this latter element is driven in rotation by the crown ring within the casing.
This device makes it possible to limit the torque due to substantial overloads on the starter However, it does not make it possible to protect the elements of the starter against moderate torque oscillations. These moderate oscillations do not entail the immediate breaking of the crown ring or of another element of the planetary gear train, but cause wear by fatigue which may, for example, cause the breaking of a tooth of a toothed element.
Certain devices propose using damper elements. The European patent EP-A-0.529.456 thus proposes a starter which includes a torque-limiter device as well as a damper.
The crown ring of the planetary gear train then includes two circular chambers separated by a transversely oriented partition. The inner annular periphery of one of the chambers carries teeth which interact with the toothing of the satellite gears. The inner annular periphery of the other chamber, for its part, includes recesses which make it possible to accommodate elements made of damping material. Axial claws of a transverse disc are inserted into the elements made of damping material. The transverse faces of the disc are in contact, on the one hand, with a transverse face of the casing and, on the other hand, with a friction ring which is pressed elastically towards the disc.
When the crown ring is subjected to moderate torque variations, each damping-material element is compressed between a claw and an opposing side face of a recess in such a way as to damp the oscillations and to limit the fatigue of the elements of the planetary gear train.
When the torque is more substantial and exceeds the value of the resisting torque, due to the friction of the disc on the friction ring and the casing, the disc is no longer immobilised; the crown ring then drives it in rotation.
Although the device proposed in this document makes it possible to damp the moderate variations in torque as well as substantial overloads on the starter, this solution entails a substantial axial bulk, as well as complicated machining operations, especially of the crown ring. This is because it requires two chambers to be produced, one including the drive teeth, and the other the recesses intended to accommodate the damping-material elements.
Moreover, this device cannot be transposed into a friction-type torque-limiter device in which the crown ring of the planetary gear train is held axially under pressure between two flanges.
The object of the invention is to propose a new design of a starter including a torque-limiter and damper device which remedies the drawbacks which have just been set out.
To this end, the invention proposes a motor-vehicle starter of the type including an electric motor the output shaft of which rotationally drives a coaxial inertia-type drive with the interposition a step-down planetary gear train including a cylindrical casing within which the crown ring, internally toothed, of the planetary gear train is mounted so as to rotate, and of the type in which the crown ring is linked in rotation to the casing by way of a friction-type torque-limiter device which is interposed axially between the crown ring and a lateral flange of the casing and which consists of at least one annular, friction side face of the crown ring and of a disc which is linked in rotation to the casing, which are pressed axially and elastically against one another by an elastic element bearing axially on a reaction surface of the disc, characterised in that the disc is linked in rotation to the casing by way of at least one damper block, elastically deformable, which absorbs mechanical energy when it is compressed, in such a way as to damp the variations in torque transmitted to the crown ring.
According to other characteristics of the invention:
the resisting torque, due to the friction, between the reaction surface of the disc and the elastic element is less than the torque between the disc and the crown ring;
the casing, in its inner periphery, includes at least one axial recess which is limited in angle, and in which is lodged at least one damper block;
the disc, at its outer periphery, includes at least one lug which carries at least one compression tab extending axially inside the axial recess, and in that [sic] the damper block is interposed in an angular way between at least one axial face of a compression tab and an opposing side face of the axial recess;
each compression tab is interposed in an angular way between two damper blocks lodged in the same axial recess;
the two damper blocks are produced as a single damper element including an axial slot in which the compression tab is accommodated;
the disc is a component made from cut-out and folded sheet metal with the lug and the compression tab produced as a single piece;
each compression tab is accommodated between two adjacent blocks so as to interact with one or the other depending on the direction of rotation of the starter;
the damper block is made of elastomer material;
the damper block includes protrusions, on an axially oriented side face, so as to provide an energy-absorption capability which is variable as a function of the compression of the damper block along a substantially tangential direction;
several damper blocks are distributed over an angle;
the damper blocks are linked together so as to constitute an annular sleeve;
an intermediate ring is interposed between the disc and the elastic element, and in that [sic] the resisting friction torque between the ring and the disc is less than the torque between the disc and the crown ring;
the ring is prevented from rotating with respect to the casing.